The invention relates to an apparatus for driving an artificial heart, and more particularly to an artificial heart driving apparatus in which positive pressure and negative pressure are alternately applied to the artificial heart using a fluid such as air thereby to drive the same.
From the standpoint of safety, it is important for artificial hearts to be driven so that a pulsatory motion closely similar to pulsation of hearts in living bodies is imparted to blood. There are known a variety of artificial hearts, such as diaphragm type, sack type, piston type, which are usually driven by receiving the predetermined pressure from a fluid such as air. To drive those artififical hearts under the optimum conditions in accordance with the state of living bodies, it is essential to employ a driving apparatus which can generate correct pressure in accordance with the optimum conditions at proper timing. In other words, such a driving apparatus is preferable that is able to correctly and quickly set heart rate, positive pressure, negative pressure and duration or duty ratio of positive pressure and negative pressure applied to artificial hearts, etc. at the respective predetermined values.
In the prior artificial heart driving apparatus, mechanical pressure reducing valves or the like are used respectively in positive and negative pressure systems as means for attaining correct pressures. However, since outputs of both positive and negative pressure systems are interconnected to each other and hence negative pressure acts as a load for the positive pressure system, whereas positive pressure acts as a load for the negative pressure system, the foregoing artificial heart driving apparatus has a disadvantage such that adjustment of positive pressure varies a load for the positive pressure system and this results in changes of positive pressure, whereas adjustment of positive pressure varies a load for the negative pressure system and this results in changes of negative pressure. In the past, therefore, when adjusting pressures, the adjustment had to be carried out carefully even in the case of adjusting either one pressure in such a manner that a pair of two pressure reducing valves are operated at the same time while checking two levels of both pressures and one pressure is maintained at the pre-determined value while updating a level of the other pressure. This results in the time-consuming pressure adjustment which also requires a great deal of skill. Moreover, the mechanical pressure reducing valves can not provide satisfactory performance, unless differential pressure between the inlet side and the outlet side is set to be relatively large. Thus, the pressure generated by a pressure source such as a compressor must be set as twice as that to be applied to artificial hearts. This leads to other disadvantages in that a large-sized pressure source is needed and levels of heating, noise, etc. are increased.
Meanwhile, the artificial heart driving apparatus of this kind is often used for a long period of time in succession. In such case, even if a part of the apparatus experiences trouble, the artificial heart can not be stopped in its driving. But when there occurs a trouble or anomaly, continued operation of the failed driving apparatus makes it impossible to drive the artificial heart under the best condition. Further, even in the case where no trouble or anomaly is observed from the outside, routine maintenance is necessary for internal parts of the apparatus. Accordingly, when carrying out maintenance, repairs, etc, up to now, another artificial heart driving apparatus is prepared and the previous driving apparatus is replaced by a new one by changing over a number of valves, cocks, etc. in the predetermined sequence in order that the artificial heart will never be stopped. But, when so many valves, cocks, etc. are changed over manually by operators, so it is impossible to absolutely eliminate a fear of switching those parts in wrong sequence. Also, at the time of exchanging the artificial heart driving apparatus, both apparatus are out of timing from each other in their drivings, whereby this exchange is accompanied with a highly possible danger.
In addition, the artificial heart driving apparatus of this kind must be equipped with a number of devices and units such as a compressor, vacuum pump, tank (accumulator), solenoid valve, control unit, etc., thus resulting in the large size. For example, artificial hearts are used as auxiliaries for the hearts of living bodies during a surgical operation, but the large-sized artificial heart driving apparatus can not be disposed near the operating table during an operation, because there are many doctors and operating equipment around the operating table. On the other hand, the artificial heart must be desirably varied in its heart rate, etc. in accordance with condition of the patient under an operation. Therefore, the prior artificial heart driving apparatus is placed at a position spaced from the operating table and then controlled by technical experts under instructions from the doctors. But, in order to drive the artificial heart under the optimum conditions, it is preferable that the driving apparatus is directly controlled by the doctors. Since the artificial heart driving apparatus in the past employs the mechanical pressure reducing valves or the like, it was difficult to realize such direct control and impossible to perform remote control.
There has been proposed another artificial heart driving apparatus in which solenoid valves to effect opening and closing control are respectively attached at the output end of a positive pressure system and the output end of a negative pressure system for switching positive and negative pressures to be applied to artificial hearts. In the apparatus of this kind, the solenoid valves are controlled by a control unit so that opening and closing are alternately switched at the predetermined timing in accordance with the preset heart rate. However, such artificial heart driving apparatus is disadvantageous in that occurrence of noise can not be avoided, because the solenoid valves are driven to be opened and closed alternately at all times. Sound-proofing covers or the like may be placed around the solenoid valves so as to suppress a level of noise, but this results in an increase of the size and cost and the apparatus becomes hard to move.